The present invention relates to the field of fluid centrifuging and in particular to the centrifuging of blood specimens.
In the practice of medical analysis it is common to submit human blood samples to analysis for the concentrations of a large number of blood components useful in diagnosis and preventive medicine. To perform these analyses, it is common to separate whole blood into the components of plasma and particulates such as blood cells or to separate coagulated or clotted blood into serum and the solids as well by centrifuging. In centrifuging the serum or plasma is lighter in weight and collects radially closer to the spin axis of the centrifuged container. The container normally used has been a test tube, several of which are supported in a hub that is spun at speeds up to and slightly over three thousand revolutions per minute. Great care is needed to insure that the spinning hub is balanced, or the combined weight of test tube and contents, along with the hub can create a dangerous, uncontrolled vibration or worse.
Processing times for centrifuging blood by this technique typically run into as long as ten (10) or twenty (20) minutes. These times are unacceptable in many emergency conditions or to permit efficient analysis on a routine basis of a great many blood samples.
Typical approaches to blood centrifuging include use of a test tube that contains the blood sample which is in turn exposed to centrifuging in a rotary hub. The plasma or serum of the centrifuged sample is then removed by a withdrawing needle or other means. Care must be exercised to prevent the remixing of the centrifuged material before extracting of the component to be analyzed. A gel material may be added to help prevent this remixing.
The test tube system also suffers from the requirement that carefully measured amounts of the blood must be placed into the tube or tubes to be centrifuged in order to prevent the unbalanced rotation of the centrifuging hub. Such care adds to the time required to centrifuge blood and cuts down on the throughput of sample analysis.
More recently, cassette designs have been placed in use involving a rotating disk that has a circular valve separating radially separated compartments which opens under centrifuging forces to permit the heavier material to collect outwardly. Such cassette techniques also require many minutes, typically twenty (20), for the separation of blood. Initial mass unbalance conditions limit the centrifugal force that can be developed in such disks without causing vibration damage. Additionally, manufacturing tolerances are strict in order to maintain the rotational balance necessary for proper operation. This in turn makes such systems costly.
In addition, liquid clarification systems are in use using a high speed air bearing rotor. Such designs are not suitable for the centrifuging of such specimens as blood, and are extremely high cost.